Functional Analysis Of Psb27 Photosynthetic Mutant In Arabidopsis Thaliana

The photosystem II (PSII) complex is located in the thylakoid membrane of higher plants, algae and cyanobacteria and drives the water oxidation process of photosynthesis, which splits water into reducing equivalents and molecular oxygen by solar energy. The by-product of photosynthesis, oxygen, has enabled life to move from the oceans to land. The PSII supracomplex consists of more than 25 different protein subunits, binding about 250 Chl, however, among which there are at least 18 low molecular mass (<10 kDa)subunits. The location and function in higher plants within PSII, still remains to be resolved.Psb27 is a newly identified lumen protein associated with PSII. Predictions of the secondary structure of the Psb27 show that the mature protein does not have any transmembrane helix. To gain insight into the function of Psb27, we isolated a mutant Arabidopsis plant with a loss of psb27 function. The quantity of PSII complexes and electron transfer within PSII remain largely unaffected in the psb27 mutant. Our results also showed that under high light illumination,PSII activity and the contents of the PSII reaction center Dl protein decreased more significantly in the psb27 mutant than in wild-type(WT)plant. Treatment of leaves with a chloroplast protein synthesis inhibitor resulted in similar light-induced PSII inactivation levels and Dl protein degradation rates in the WT and psb27 knockout plants. Recovery of PSII activity after photoinhibition was delayed in the psb27 mutant, suggesting that Psb27 is required for efficient recovery of the photodamaged PSII complex.Overall, these results demonstrated that the Psb27 protein in Arabidopsis is not essential for oxygenic photosynthesis and PSII formation. Instead, our results provide evidence for the involvement of this lumen protein in the recovery process of PSII.